This invention describes an apparatus which provides a leveling action for keys, such as those used in keyboards for notebook and other computing applications.
It is known to use levelers for keys in certain keyboard applications. In particular, levelers have been used in conjunction with multi-unit keys such as the "space bar" and "enter" keys. These keys are known as multi-unit keys because they typically occupy more space than the standard one unit alphanumeric keys such as "A" and "1" which comprise most of the keys on a keyboard of standard construction. Quite frequently, these keys occupy multiples of the footprint or area occupied by a standard key, hence the term multi-unit key. One well known problem associated with multi-unit keys is the problem of binding or sticking during actuation of the key. Typically, keys are constructed with either a single key stem, or multiple key stems attached to the back surface of the keycap and a corresponding key guide portion, or portions, which extends upwardly from a base in order to engage the key stem, as illustrated in FIG. 1. In contrast with single unit keys, multi-unit keys are capable of being actuated by forces which are not substantially aligned with the longitudinal axis of a key stem as also illustrated in FIG. 1. Such off-axis forces have a tendency to cause the key stem to be canted within the key guides such that the longitudinal axis of the key stem and key guide are no longer aligned parallel to one another. This causes the key stem to rub against the side of the key guide, thereby causing binding or sticking of the key. One solution to this problem has been to incorporate keycaps with multiple key stems and associated multiple key guides. This is not always a practical solution, however, because it has been found that the additional key stems and key guides must have a certain minimum length in order to operate effectively and prevent binding or sticking. In many cases, the minimum length required produces a key which has an overall thickness which is greater than desired for a particular keyboard application. The net effect is to increase the overall thickness of the keyboard, which is usually commercially undesirable.
In order to permit the construction of reliable, thinner keyboards, key levelers have been utilized, such as shown in FIG. 1. In a conventional multi-unit key 2, leveler 4 comprising a generally U-shaped rod 6 is utilized. Leveler 4 is rotatably attached to both ends 8 of lower surface 10 of keycap 12. As key 2 is assembled, key stems 14 are inserted into key guides 16 and leveler 4 is slidably and rotatably engaged with the base 18 which contains key guide 16. As key 2 is actuated off the longitudinal axis of key stem 14 by a force F, the portion of leveler 4 engaged in base 18 closest to the applied force F is displaced by a sliding motion within the base. This displacement also causes a similar sliding displacement of the opposing end of leveler 4 within the base and produces a downward force on the opposing end of keycap 12. The net effect is that the leveler 4 prevents canting of the keycap due to off-axis actuation forces and thereby prevents binding of the key stem 14 within key guide 16.
One problem with leveler structures of the type described above is that they require sufficient space to attach the leveler on both ends of the key and to sufficiently engage the leveler with the base. Referring again to FIG. 1, in some applications, such as notebook computer applications, the size of the elastomeric boot 19 which is commonly used as a return spring for the key, does not permit enough space to utilize a conventional leveler. In such applications, the boot dome may be located around the circumference of the key guide, rather than underneath the key guide as is often the case in keyboards of conventional construction. The diameter of the base of such elastomeric boot domes may be on the order of 0.675 inches, as opposed to a diameter on the order of 0.500 inches as is typical in conventional keyboard construction. The additional space required for the elastomeric boot dome decreases the amount of space available for additional structures under the keycap, such as a leveler. Also, the overall keycap profile, including height, width and length, in notebook keyboards may be substantially smaller than the key profile allowable in conventional keyboard construction. This further limits the amount of space available under the key to incorporate additional mechanical structures such as a leveler.